September 2009

In the Moment: Sports Medicine 1683496 1683496


by Jordana Bieze Foster

Seeking a fatigue-injury link

Do studies really mimic game situations?

Even as some researchers inch closer to an understanding of how fatigue increases risk of injury, others are suggesting that accepted methods of studying the problem may be flawed.

Epidemiologic data from a number of sports indicates that injury rates are highest near the end of a game or near the end of a period of play, suggesting that fatigue exacerbates existing risk factors for injury. Researchers have proposed that physical fatigue alters biomechanics, whether by affecting muscle strength or activation, or that mental fatigue alters an athlete’s reaction time and decision-making ability.

Findings from the University of Wisconsin-Milwaukee, presented in late August at the annual meeting of the American Society of Biomechanics, suggests decision-making may not play a significant role in the fatigue-injury equation. The researchers assessed knee dynamics during cutting maneuvers as well as decision-making skills in 10 female soccer players, before and after a 60-minute soccer-specific exercise protocol designed to simulate a full-length game.

The investigators found had a significant effect of fatigue on knee internal rotation angle, and a trend toward significance for knee flexion angle and peak flexion moment. However, fatigue had no effect on the athletes’ reaction time or decision-making accuracy as measured by the Eriksen-Flanker test.

Fatigue was also found to significantly affect knee mechanics in a study from the University of Michigan, which was published in the August issue of Medicine & Science in Sports & Exercise. The Michigan researchers analyzed hip and knee mechanics during single-leg landings in 20 female collegiate athetes, before and after a fatigue protocol that involved repeated single-leg squats.

Fatigue significantly affected knee flexion angle at initial contact and knee flexion moment, hip internal rotation and knee abduction angles and moments at peak stance. The Michigan researchers also found that fatigue effects were more pronounced during unanticipated landings than anticipated landings, in contrast to the Wisconsin-Milwaukee group’s finding of no significant interaction between anticipation and fatigue.

Interestingly, the Michigan group found that although only one limb was involved in the fatigue protocol, the effects of fatigue were seen in both limbs equally—suggesting that a central fatigue mechanism is at work.

However, another study presented at the ASB meeting suggests that the fatigue protocol used in the Michigan study may not accurately reflect the type of fatigue experienced by athletes during a game situation. Researchers from Arizona State University compared the effects of three fatigue protocols on landing mechanics (from a maximal vertical jump) and knee position sense in 12 active college students, half of whom were female. One protocol involved a 15-20 minute full-court basketball game, one involved repeated squats, and the third involved five minutes of intense treadmill running.

In terms of effect on both landing mechanics and knee position sense, the running protocol was most similar to the basketball protocol. Peak knee flexion angle was significantly increased following the running and squat protocols, and trended toward significance following the basketball protocol. But normalized ground reaction force decreased significantly following the squat protocol only, suggesting that effect is task-specific. Similarly, the squat protocol was the only one not associated with a significant increase in knee positioning error.

Further complicating the issue, an Australian study of 14 male volleyball players found that the biomechanical effects of fatigue differed significantly between a drop landing, of the type commonly used in studies, and landing from a volleyball spike jump. That study, published in the July issue of the Scandinavian Journal of Medicine & Science in Sports, suggests researchers might want to explore alternative landing tasks that more closely replicate sport-specific situations.

Baseball data confirm speed benefits of running through bases vs sliding

Baseball managers everywhere will nod knowingly, but a study from Indiana University confirms that running through a base is faster than sliding and that sliding is faster than running to a stop. What remains unclear, however, is whether a head-first slide is faster than a feet-first slide.

The study, presented in August at the annual ASB meeting, analyzed nine collegiate baseball players running between first and second base using the four techniques. All significant differences in velocity occurred during the last 10 m.

Running through (RT) was significantly faster than the three others in terms of actual velocity of the center of mass, and running to a stop was significantly slower than the three others. But in terms of effective velocity, which accounts for the “final reach” before the COM has reached base, RT was not significantly faster than head first, which was not significantly faster than feet first(FF). Feet first, however, was significantly slower than RT, which suggests that the head first technique lies somewhere between RT and FF.

Time away from volleyball affects postural control, increases injury risk

Detraining in volleyball players, whether stemming from injury or the need for some off-season rest and relaxation, can significantly decrease postural stability and increase the risk of ankle sprain, according to research from Iowa State University.

Investigators analyzed stabilometric performance in 12 female collegiate volleyball players at the conclusion of a competitive season and again one month later. During that time, training frequency decreased from 20 hours per week to fewer than three hours per week.

After detraining, the athletes demonstrated significant increases in medial-lateral, anterior-posterior, and overall center of pressure velocity during a single leg stance with eyes closed. Standing time, COP area, and COP standard deviation did not change significantly.

The results, presented in August at the annual ASB meeting, suggest that the athletes’ stabilometric abilities suffered in the absence of the continual strengthening and proprioceptive stimulation provided during the season. Because impaired postural control is a risk factor for ankle sprain, athletes may benefit from balance exercises following detraining in order to decrease their risk of injury.

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